Food storage refrigerators of conventional design present two major problems. The first arises because home refrigerators use energy at the times when the utility company that supplies that energy experiences its peak load. Most, if not all, utility power companies are called upon to supply energy at a much higher rate during some periods of the day than at other periods. Thus, for example, the mid-afternoon demand on a weekday may be several times the demand at night and on weekends. Suppliers of energy must provide facilities at major capital cost which are capable of meeting the peak demands for energy. The result is that costly energy conversion and distribution facilities operate at far below capacity much of the time. The cost of energy at the point of use is necessarily much greater than it could be if those facilities were used more efficiently. Further, under present and proposed time-of-day rates for electrical energy, the cost to the refrigerator owner of energy used during peak periods is several times greater than at other times.
For many energy suppliers, the energy used in home refrigerators represents a very significant part of the total load. Very substantial and important savings could be realized if the load represented by home refrigerators were to be shifted to periods of low demand. That can be, and has been, done by powering refrigerators from circuits that are simply de-energized during the supplying utilities' peak demand periods. However, that solution can result in spoiling of food and a health hazard with present refrigerator designs.
Inefficiency per se is the second of the two major problems presented by conventional refrigerator designs. In the conventional system, the entire refrigeration system, both refrigerant circuit and air flow circuit, is governed by sensing ambient air temperature within the refrigerator box. Each time the door is opened, the ambient temperature increases. Unless the period of door opening is very short, the temperature sensor will demand cooling, the compressor motor, which accounts for over 80% of the electrical energy required for refrigerators, will be turned on, and the in-rush current to the motor will be high. In that cycle, which may be repeated many times, there is energy waste in frequent start-up followed by a short interval running time. The result for the refrigerator owner is excessive use of energy resulting in higher cost. The national result is waste of a limited resource. Moisture control of condensation on the exterior of the refrigerator enclosure and of frost on the surface of the evaporator usually accounts for over ten percent of the electrical energy used in refrigerators. The conventional defrost control consists of a timer which, on a set time cycle, energizes an electric heater which removes frost by convective and radiant heating of the entire evaporator body to a temperature sufficient to melt the frost. Timing intervals and on periods of these systems are pre-set and must be based on defrosting under worst case conditions without regard to the actual presence or absence of frost, wasting energy. Similarly, heaters used to eliminate the moisture of condensation on the exterior of the enclosure operate on a set basis without regard for actual conditions, wasting energy. Past efforts to solve the efficiency problem in refrigerators have been directed primarily to providing better insulation, and to providing more efficient compressors and evaporators.
This invention reduces the total energy required for residential refrigeration and shifts the demand for the energy occurring during high-cost peak periods to other times of lesser demand and cost, and it provides that contribution in new dimensions.
The residential refrigerator requires sixteen percent of all of the oil imported into the United States from the Middle East. Test results demonstrate that this invention provides the potential to remove as much as twenty-five percent of that requirement.